Description of the Prior Art
Various methods have been described for the removal of sulfur dioxide from a waste gas stream. Sulfur dioxide is an environmental pollutant that is implicated as the chief source of acid rain. Among the methods for controlling SO.sub.2 may be mentioned the methods described in U.S. Pat. Nos. 3,515,513 3,523,755, 3,542,511, 3,510,923, 3,475,122, 3,655,547, 4,059,496, 4,306,950, 4,421,726, and 4,528,173.
A majority of these methods resort to the use of alkaline solutions containing sodium or lime to remove sulfur dioxide. Others propose to oxidize sulfur dioxide with air or oxygen using catalysts to promote the reaction. Additional processes make use of oxidizing reagents such as hypochlorite to convert sulfites to sulfates.
The available emission control methods present certain technical difficulties and economical disadvantages. The alkaline scrubbing processes produce waste products that are useless and a problem to dispose of. In the catalytic processes, the catalysts may become fouled and lose their activity. Oxidizing reagents are costly, require precise metering, and are thermally unstable.
It is therefore an object of the present invention to provide a process for the removal of sulfur dioxide from waste gases that overcomes the disadvantages of the conventional methods.
It is also an object to provide a process for the recovery of sulfur values from vent or flue gas as a valuable by-product while avoiding an air pollution problem.
It is a further object to provide a process of the kind mentioned which is relatively economical and does not require the use of catalysts or oxidizing reagents.
These and other objects, features and advantages of the invention will be apparent from the accompanying drawing and the following description.